1. Field of the Invention
This invention generally relates to internal combustion engines and more particularly relates to marine engines capable of detection of sea water infiltrating into its combustion chamber.
2. Description of the Related Art
Because water is more likely to be mixed in fuel used for the driving of the engine in watercraft outboard motors than in motor vehicles, due to the condition of use in which the watercraft run on the water in the sea or a river, and because the engine function might be damaged if water is mixed in the fuel, there has been provided a device for detecting water infiltrating a fuel tank or the like. The goal is to prevent possible damage to the engine.
As devices for detecting such ingress of water, systems have been known which are disclosed in JP-A-2000-27723 and JP-A-2000-064938. In JP-A-2000-27723, reference is made to a fuel filter disposed in a fuel feed system in a marine engine, wherein said fuel filter comprises a filter body; a filter case mounted detachably to the filter body; a filter material disposed in the filter case; and a float type water detection sensor disposed below the filter material.
According to this patent document, it is stated that this device does not lower separating properties of water due to vibration, and the water level can be detected exactly.
On the other hand, in JP-A-2000-064938, reference is made to an ion current detection device for internal combustion engines comprising ion current measurement means for measuring an ion current in response to the number of ions produced by a mixture burning in a cylinder of the internal combustion engine; humidity detection means for detecting the humidity of the atmosphere; and correction means for correcting the ion current value measured by the ion current measurement means in response to the humidity detected by the humidity detection means.
According to this patent document, it is stated that an ion current value exactly reflecting the burning condition can be detected irrespective of humidity fluctuations.
However, since in the invention described in JP-A-2000-27723, the float provided in the fuel filter moves during operation of the watercraft on the water, the float type water detection sensor might malfunction and provide false detection of an infiltration of sea water, even when there has been no infiltration of water.
In the invention described in JP-A-2000-064938, it is stated that when a mixture is burned in a cylinder of an internal combustion engine, the ion current in the cylinder is measured to judge the air fuel ratio. However, it does not disclose judging from the ion current measurement whether or not there has been an infiltration of sea water in a marine engine.